1. Field of the Invention
This invention relates generally to an improved shutter blade encoding system and, more particularly, to an improved shutter blade encoding system for a shutter blade arrangement of the so-called scanning type.
2. Description of the Prior Art
One well-known exposure control mechanism for a photographic camera is a so-called scanning blade shutter comprising two cooperatively moving shutter blade elements connected for opposed reciprocating movement with respect to each other. The shutter blade elements are formed with selectively shaped aperture openings which, depending upon the position of the blades, symmetrically overlap over a light entry exposure opening within the camera housing. The blade elements are connected to define a progression of apertures over the light entry opening in the camera as a result of their connection with a so-called "walking beam" or actuator which is rotatably mounted with respect to the camera housing. Thus interconnected, the shutter blade elements move simultaneously and in correspondence with each other to define a symmetrically configured and variable aperture opening over the camera light entry exposure opening.
In shutter blade arrangements of the abovedescribed type, it is often necessary to electronically track the exact position of the shutter blade elements during the exposure interval. Toward this end, there have been provided shutter blade encoding systems of a type as is disclosed in U.S. Pat. No. 4,053,907, entitled "Program Controlled Shutter", by H. Iwata et al., issued Oct. 11, 1977. The aforementioned encoding system comprises a plurality of aligned slits on one of the shutter blade elements disposed intermediate a light source and a photocell so that movement of the aligned slits between the light source and photocell provide an output signal waveform indicative of the instantaneous position of the shutter blade element. The resolution or accuracy at which the instantaneous position of the shutter blade element may be determined depends upon the width and spacing of the slits which can be provided in the shutter blade elements as well as the width of the photocell which cannot exceed the width of one slit. Thus, in exposure control systems where a high degree of resolution or accuracy is desired as to the determination of the instantaneous blade position, it may not be possible or practical to make sufficiently thin slits as well as a sufficiently small photocell to provide the degree of accuracy required.
Therefore, it is a primary object of this invention to provide an improved shutter blade encoding system in which the resolution or degree of accuracy at which the blade position may be determined is doubled without incurring a decrease in the width of the slits heretofore provided in shutter blade encoding systems.
It is a further object of this invention to provide an improved shutter blade encoding system in which the overall size of the photoresponsive element may exceed the width of an individual slit and may even overlap a plurality of slits.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.